Telecommunications method and system

ABSTRACT

A mobile communications system for communicating data to and/or from mobile units, the system comprising one or more base stations arranged to communicate data to or from the mobile units via a wireless access interface within one or more frequency bands, and one or more of the base stations is arranged to provide a plurality of logically separate carriers for transmitting data to mobile units, wherein each of the logically separate carriers comprises physical communications resources within the one or more frequency bands of the wireless access interface; a first group of one or more mobile units arranged to communicate with the one or more base stations via at least a first carrier of the plurality of carriers; and a second group of one or more mobile units arranged to communicate with the one or more base stations via at least a second carrier of the plurality of carriers. The one or more base stations are operable to provide common information on the first carrier, the common information being for at least one mobile unit in the first group and for at least one mobile unit in the second group. The one or more base stations are operable to provide allocation information in the first carrier, the allocation information comprising an indication of the location of the common information within the first carrier. The one or more base stations are further operable to provide allocation information in the second carrier, the allocation information comprising an indication of the location of the common information within the first carrier. At least one mobile unit in the second group is arranged, upon reception of the allocation information in the second carrier, to access the common information provided by the one or more base stations in the first carrier.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application which claims thebenefit of priority under 35 U.S.C. §120 of U.S. patent application Ser.No. 14/125,831, filed Jan. 7, 2014, which is based on PCT/GB2012/051326,filed Jun. 12, 2012, and claims priority to British patent applicationno. 1109986.8, filed Jun. 14, 2011; the entire contents of each of whichare incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to methods, systems and apparatus forcommunicating data in a mobile communications system.

BACKGROUND OF THE INVENTION

Third and fourth generation mobile telecommunication systems, such asthose based on the 3GPP defined UMTS and Long Term Evolution (LTE)architecture are able to support more sophisticated services than simplevoice and messaging services offered by previous generations of mobiletelecommunication systems.

For example, with the improved radio interface and enhanced data ratesprovided by LTE systems, a user is able to enjoy high data rateapplications such as mobile video streaming and mobile videoconferencing that would previously only have been available via a fixedline data connection. The demand to deploy third and fourth generationnetworks is therefore strong and the coverage area of these networks,i.e. geographic locations where access to the networks is possible, isexpected to increase rapidly.

The anticipated widespread deployment of third and fourth generationnetworks has led to the parallel development of a class of devices andapplications which, rather than taking advantage of the high data ratesavailable, instead take advantage of the robust radio interface andincreasing ubiquity of the coverage area. Examples include so-calledmachine type communication (MTC) applications, which are typified bysemi-autonomous or autonomous wireless communication devices (i.e. MTCdevices) communicating small amounts of data on a relatively infrequentbasis. Examples include so-called smart meters which, for example, arelocated in a customers house and periodically transmit information backto a central MTC server data relating to the customers consumption of autility such as gas, water, electricity and so on. Such MTC devices maytherefore communicate using a different network to the conventionalterminals where the networks can be more adapted to the needs of MTCdevices or conventional terminals. As each of MTC devices andconventional devices then use a different autonomous network, someinformation may be duplicated in each network.

Also, systems where a terminal may be connected to more than one carrierare starting to emerge. For example a terminal may communicate with abase station via two separate carriers so that it can increase itsthroughput. The terminal then uses each of the two carriers in a mannersimilar to a single-carrier situation. Other terminals may be connectedto only one of these two carriers and, in effect, these carriers are notexclusive to terminals using more than one carrier. Each of thesecarriers therefore has to be able to function autonomously from theother carriers. For example, the carrier has to provide the carriercontrol information and any carrier-management related informationrelevant to the terminals so that it is available to the terminals usingthis carrier only.

In situations where more than one carrier is provided, each of thesecarriers are usually expected to function autonomously from each otherand they therefore comprise their own carrier-management information andany other broadcasted information or data so that a terminal connectedto this carrier only can always be given access to the information ordata in the carrier. In some situations, in order to ensure that each ofthese carriers may be autonomously used by a terminal, there may bepartial or complete duplication of such data in two or more carriers.

SUMMARY OF THE INVENTION

Various aspects and features of the present invention are defined in theappended claims.

In the example of MTC devices, whilst it can be convenient for aterminal such as an MTC type terminal to take advantage of the widecoverage area provided by a third or fourth generation mobiletelecommunication network there are at present disadvantages. Unlike aconventional third or fourth generation mobile terminal such as asmartphone, an MTC-type terminal is preferably relatively simple andinexpensive. The type of functions performed by the MTC-type terminal(e.g. collecting and reporting back data) do not require particularlycomplex processing to perform. However, third and fourth generationmobile telecommunication networks typically employ advanced datamodulation techniques on the radio interface which can require morecomplex and expensive radio transceivers to implement. It is usuallyjustified to include such complex transceivers in a smartphone as asmartphone will typically require a powerful processor to performtypical smartphone type functions. However, as indicated above, there isnow a desire to use relatively inexpensive and less complex devices tocommunicate using LTE type networks. There can therefore be providedcarriers for devices having limited capabilities, where these carriers(sometimes called “virtual carriers”) are provided within a largercarrier (sometimes called “host carrier”). In that respect, the readeris directed to our co-pending UK patent applications numbers: 1101970.0,1101981.7, 1101966.8, 1101983.3, 1101853.8, 1101982.5, 1101980.9 and1101972.6, the contents of which are incorporated herein by reference.The virtual carrier may for example be used mainly by MTC type deviceswhile the host carrier may be mainly used by conventional terminals. Thehost and virtual carriers may for example be provided in an independentmanner. In such an example, the terminals connected to the host carrierare not aware or directly affected by an eventual virtual carrier withinthe host carrier, while terminals connected to the virtual carrier areunaware of the host carrier configuration, or data. In effect, eventhough the virtual carrier is provided within a host carrier, these twocarriers are logically separate and each carrier is an autonomouscarrier. For example, they may each comprise their own controlinformation and any carrier-management related information relevant totheir respective terminals.

According to an aspect of the invention, there is provided a mobilecommunications system for communicating data to and/or from mobileunits, the system comprising one or more base stations arranged tocommunicate data to or from the mobile units via a wireless accessinterface within one or more frequency bands, and one or more of thebase stations is arranged to provide a plurality of logically separatecarriers for transmitting data to mobile units, wherein each of thelogically separate carriers comprises physical communications resourceswithin the one or more frequency bands of the wireless access interface;a first group of one or more mobile units arranged to communicate withthe one or more base stations via at least a first carrier of theplurality of carriers; and a second group of one or more mobile unitsarranged to communicate with the one or more base stations via at leasta second carrier of the plurality of carriers. The one or more basestations are operable to provide common information on the firstcarrier, the common information being for at least one mobile unit inthe first group and for at least one mobile unit in the second group.The one or more base stations are operable to provide allocationinformation in the first carrier, the allocation information comprisingan indication of the location of the common information within the firstcarrier. The one or more base stations are further operable to provideallocation information in the second carrier, the allocation informationcomprising an indication of the location of the common informationwithin the first carrier. At least one mobile unit in the second groupis arranged, upon reception of the allocation information in the secondcarrier, to access the common information provided by the one or morebase stations in the first carrier.

There has therefore been provided a system where allocation informationis provided in two different and logically separate carriers, whereinthe allocation information in each of the carriers comprises anindication of the location of common information in one of the carriers.As a result, the amount of resources allocated to transmit theinformation has been reduced by sending information common to two ormore carriers in one carrier. Thus the total throughput available viathe carriers for other information has been increased.

According to another aspect of the invention, there is provided a methodfor communicating data in a mobile communications system, wherein thesystem comprises one or more base stations arranged to communicate datato or from the mobile units via a wireless access interface within oneor more frequency bands, and one or more of the base stations beingarranged to provide a plurality of logically separate carriers fortransmitting data to mobile units, wherein each of the logicallyseparate carriers comprises physical communications resources within theone or more frequency bands of the wireless access interface. The systemfurther comprises a first group of one or more mobile units arranged tocommunicate with the one or more base stations via at least a firstcarrier of the plurality of carriers; and a second group of one or moremobile units arranged to communicate with the one or more base stationsvia at least a second carrier of the plurality of carriers. The methodcomprises providing common information on the first carrier, the commoninformation being for at least one mobile unit in the first group andfor at least one mobile unit in the second group; providing allocationinformation in the first carrier, the allocation information comprisingan indication of the location of the common information within the firstcarrier; providing allocation information in the second carrier, theallocation information comprising an indication of the location of thecommon information within the first carrier; and at least one mobileunit accessing the common information provided in the first carrier uponreception of the allocation information in the second carrier.

According to a further aspect of the invention, there is provided anetwork apparatus for communicating data to and/or from mobile units,the apparatus being arranged to provide a wireless access interfacewithin one or more frequency bands to communicate data to or from themobile units; provide a plurality of logically separate carriers fortransmitting data to mobile units, wherein a carrier comprises physicalresources within the one or more frequency bands of the wireless accessinterface, wherein the apparatus is further arranged to provide a firstcarrier of the plurality of carriers to communicate with a first groupof one or more mobile units and a second carrier of the plurality ofcarriers to communicate with a second group of one or more mobile units.The apparatus is arranged to provide common information on the firstcarrier, the common information being for at least one mobile unit inthe first group and for at least one mobile unit in the second group;provide allocation information in the first carrier, the allocationinformation comprising an indication of the location of the commoninformation within the first carrier; and provide allocation informationin the second carrier, the allocation information comprising anindication of the location of the common information within the firstcarrier.

Various further aspects and embodiments of the invention are provided inthe appended claims, including but not limited to, a network element foruse in a mobile communications network and a method of using a networkelement for communicating data to and/or from mobile communicationsdevices.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings where likeparts are provided with corresponding reference numerals and in which:

FIG. 1 provides a schematic diagram illustrating an example of aconventional mobile telecommunication network;

FIG. 2 provides a schematic diagram illustrating a conventional LTEdownlink radio frame;

FIG. 3 provides a schematic diagram illustrating a conventional LTEdownlink radio sub-frame;

FIG. 4 provides a schematic diagram illustrating a conventional LTE“camp-on” procedure;

FIG. 5 provides a schematic diagram illustrating an LTE downlink radiosub-frame in which a virtual carrier has been inserted;

FIG. 6 provides a schematic diagram illustrating an adapted LTE“camp-on” procedure for camping on to a virtual carrier;

FIG. 7 provides a schematic diagram illustrating LTE downlink radiosub-frames;

FIG. 8 provides a schematic diagram illustrating a group of sub-framesin which two virtual carriers change location within a host carrierband;

FIG. 9 provides a schematic diagram illustrating a virtual carrier and ahost carrier each comprising an allocation message linked to allocatedresources in the host carrier;

FIG. 10 provides a schematic diagram illustrating a virtual carrier anda host carrier each comprising an allocation message linked to allocatedresources in the virtual carrier;

FIGS. 11A-11C provide schematic illustrations of common informationcarried in a virtual carrier;

FIG. 12 provides schematic diagrams illustrating a virtual carrier and ahost carrier each comprising an allocation message linked to allocatedresources in the virtual carrier;

FIG. 13 provides a schematic diagram illustrating of two conventionalLTE carriers having separate frequency ranges;

FIG. 14 provides a schematic diagram illustrating two carriers, eachcomprising an allocation message linked to resources allocated in one ofthe carriers;

FIGS. 15-17 provide a schematic diagram illustrating variousarrangements comprising two carriers, wherein each carrier may comprisean allocation message linked to the resources allocated in one or theother of the carriers;

FIG. 18 provides a schematic diagram illustrating of partitioning ofcommon information in a two carrier example.

DESCRIPTION OF EXAMPLE EMBODIMENTS

The example embodiments will be generally described in the context of a3GPP LTE architecture. However, the invention is not limited to animplementation in a 3GPP LTE architecture. Conversely, any suitablemobile architecture is considered to be relevant.

Conventional Network

FIG. 1 provides a schematic diagram illustrating the basic functionalityof a conventional mobile telecommunications network.

The network includes a plurality of base stations 101 connected to acore network 102. Each base station provides a coverage area 103 (i.e. acell) within which data can be communicated to and from mobile terminals104. Data is transmitted from a base station 101 to a mobile terminal104 within a coverage area 103 via a radio downlink. Data is transmittedfrom a mobile terminal 104 to a base station 101 via a radio uplink. Thecore network 102 routes data to and from the mobile terminals 104 andprovides functions such as authentication, mobility management, chargingand so on.

Mobile telecommunications systems such as those arranged in accordancewith the 3GPP defined Long Term Evolution (LTE) architecture use anorthogonal frequency division multiplex (OFDM) based interface for theradio downlink (so-called OFDMA) and the radio uplink (so-calledSC-FDMA). Data is transmitted on the uplink and on the downlink on aplurality of orthogonal sub-carriers. FIG. 2 shows a schematic diagramillustrating an LTE downlink radio frame 201. The LTE downlink radioframe is transmitted from an LTE base station (known as an enhanced NodeB) and lasts 10 ms. The downlink radio frame comprises ten sub-frames,each sub-frame lasting 1 ms. A primary synchronisation signal (PSS) anda secondary synchronisation signal (SSS) are transmitted in the firstand sixth sub-frames of the LTE frame. A primary broadcast channel(PBCH) is transmitted in the first sub-frame of the LTE frame. The PSS,SSS and PBCH are discussed in more detail below.

FIG. 3 provides a schematic diagram providing a grid which illustratesthe structure of an example of a conventional downlink LTE sub-frame.The sub-frame comprises a predetermined number of symbols which aretransmitted over a 1 ms period. Each symbol comprises a predeterminednumber of orthogonal sub-carriers distributed across the bandwidth ofthe downlink radio carrier.

The example sub-frame shown in FIG. 3 comprises 14 symbols and 1200sub-carriers spaced across a 20 MHz bandwidth. The smallest unit onwhich data can be transmitted in LTE is twelve sub-carriers transmittedover one sub-frame. For clarity, in FIG. 3, each individual resourceelement is not shown, instead each individual box in the sub-frame gridcorresponds to twelve sub-carriers transmitted on one symbol.

FIG. 3 shows resource allocations for four LTE terminals 340, 341, 342,343. For example, the resource allocation 342 for a first LTE terminal(UE 1) extends over five blocks of twelve sub-carriers, the resourceallocation 343 for a second LTE terminal (UE2) extends over six blocksof twelve sub-carriers and so on.

Control channel data is transmitted in a control region 300 of thesub-frame comprising the first n symbols of the sub-frame where n canvary between one and three symbols for channel bandwidths of 3 MHz orgreater and where n can vary between two and four symbols for channelbandwidths of 1.4 MHz. For clarity, the following description relates tohost carriers with channel bandwidth of 3 MHz or greater where themaximum value of n will be 3. The data transmitted in the control region300 includes data transmitted on the physical downlink control channel(PDCCH), the physical control format indicator channel (PCFICH) and thephysical HARQ indicator channel (PHICH).

The PDCCH contains control data indicating which sub-carriers on whichsymbols of the sub-frame have been allocated to specific LTE terminals.Thus, the PDCCH data transmitted in the control region 300 of thesub-frame shown in FIG. 3 would indicate that UE1 has been allocated thefirst block of resources 342, that UE2 has been allocated the secondblock of resources 343, and so on. The PCFICH contains control dataindicating the size of the control region (i.e. between one and threesymbols) and the PHICH contains HARQ (Hybrid Automatic Request) dataindicating whether or not previously transmitted uplink data has beensuccessfully received by the network.

In certain sub-frames, symbols in a central band 310 of the sub-frameare used for the transmission of information including the primarysynchronisation signal (PSS), the secondary synchronisation signal (SSS)and the physical broadcast channel (PBCH). This central band 310 istypically 72 sub-carriers wide (corresponding to a transmissionbandwidth of 1.08 MHz). The PSS and SSS are synchronisation signals thatonce detected allow the LTE terminal 104 to achieve framesynchronisation and determine the cell identity of the enhanced Node Btransmitting the downlink signal. The PBCH carries information about thecell, comprising a master information block (MIB) that includesparameters that the LTE terminals require to access the cell. Datatransmitted to individual LTE terminals on the physical downlink sharedchannel (PDSCH) can be transmitted in the remaining blocks of resourceelements of the sub-frame. Further explanation of these channels isprovided in the following sections.

FIG. 3 also shows a region of PDSCH containing system information andextending over a bandwidth of R₃₄₄.

The number of sub-carriers in an LTE channel can vary depending on theconfiguration of the transmission network. Typically this variation isfrom 72 sub carriers contained within a 1.4 MHz channel bandwidth to1200 sub-carriers contained within a 20 MHz channel bandwidth as shownin FIG. 3. As is known in the art, data transmitted on the PDCCH, PCFICHand PHICH is typically distributed on the sub-carriers across the entirebandwidth of the sub-frame. Therefore a conventional LTE terminal mustbe able to receive the entire channel bandwidth in order to receive anddecode the control region.

FIG. 4 illustrates an LTE “camp-on” process, that is, the processfollowed by a terminal so that it can decode downlink transmissionswhich are sent by a base station via a downlink channel. Using thisprocess, the terminal can identify the parts of the transmissions thatinclude system information for the cell and thus decode configurationinformation for the cell.

As can be seen in FIG. 4, in a conventional LTE camp-on procedure, theterminal first synchronizes with the base station (step 400) using thePSS and SSS in the centre band and then decodes the PBCH (step 401).Once the terminal has performed steps 400 and 401, it is synchronizedwith the base station.

For each sub-frame, the terminal then decodes the PCFICH which isdistributed across the entire width of carrier 320 (step 402). Asdiscussed above, an LTE downlink carrier can be up to 20 MHz wide (1200sub-carriers) and an LTE terminal therefore has to have the capabilityto receive and decode transmissions on a 20 MHz bandwidth in order todecode the PCFICH. At that stage, with a 20 MHz carrier band, theterminal operates at a much larger bandwidth (bandwidth of R₃₂₀) thanduring steps 400 and 401 (bandwidth of R₃₁₀) relating to synchronizationand PBCH decoding.

The terminal then ascertains the PHICH locations (step 403) and decodesthe PDCCH (step 404), in particular for identifying system informationtransmissions and for identifying its personal allocation grants. Theallocation grants are used by the terminal to locate system informationand to locate its data in the PDSCH. Both system information andpersonal allocations are transmitted on PDSCH and scheduled within thecarrier band 320. Steps 403 and 404 also require the terminal to operateon the entire bandwidth R320 of the carrier band.

At steps 402 to 404, the terminal decodes information contained in thecontrol region 300 of a sub-frame. As explained above, in LTE, the threecontrol channels mentioned above (PCFICH, PHICH and PDCCH) can be foundacross the control region 300 of the carrier where the control regionextends over the range R₃₂₀ and occupies the first one, two or threeOFDM symbols of each sub-frame as discussed above. In a sub-frame,typically the control channels do not use all the resource elementswithin the control region 300, but they are scattered across the entireregion, such that a LTE terminal has to be able to simultaneouslyreceive the entire control region 300 for decoding each of the threecontrol channels.

The terminal can then decode the PDSCH (step 405) which contains systeminformation or data transmitted for this terminal.

When one or more base stations provide several carriers for transmittinginformation to mobile units, there may sometimes be an overlap in datatransmitted in each of the carriers. If for example a base station sendssystem information in two or more carriers provided by this basestation, the system information may comprise information common to thetwo carriers and there may therefore be duplication in the systeminformation transmitted in the two carriers. This duplication may beconsidered as a less than optimal use of resources and a reduction ofthis duplication may therefore be desirable.

The following two examples illustrate how this duplication may bereduced in two example situations. In the first situation two carriersare provided, one carrier being provided within the other carrier, andin the second situation two carriers are provided and havenon-overlapping frequency ranges. However the invention is not limitedto these two specific examples. It is in particular intended that atleast any situation with two or more carriers provided by one or morebase stations, where there may be duplication in data transmitted to oneor more mobile units in the first and second carriers, be considered asa suitable situation for an embodiment.

Virtual Downlink Carrier Example

Certain classes of devices, such as MTC devices (e.g. semi-autonomous orautonomous wireless communication devices such as smart meters asdiscussed above), support communication applications that arecharacterised by the transmission of small amounts of data at relativelyinfrequent intervals and can thus be considerably less complex thanconventional LTE terminals. In many scenarios, providing low capabilityterminals such as those with a conventional high-performance LTEreceiver unit capable of receiving and processing data from an LTEdownlink frame across the full carrier bandwidth can be overly complexfor a device which only needs to communicate small amounts of data. Thismay therefore limit the practicality of a widespread deployment of lowcapability MTC type devices in an LTE network. It is preferable insteadto provide low capability terminals such as MTC devices with a simplerreceiver unit which is more proportionate with the amount of data likelyto be transmitted to the terminal. This has therefore led to theemergence of a concept sometimes called “virtual carrier”, where the“virtual carrier” is inserted in a conventional downlink carrier (i.e. a“host carrier”). Unlike data transmitted on a conventional downlinkcarrier, data transmitted on the virtual carrier can be received anddecoded without needing to process the full bandwidth of the downlinkhost carrier. Accordingly, data transmitted on the virtual carrier canbe received and decoded using a reduced complexity receiver unit. Forthe sake of completeness, possible examples of a virtual carrier will bebriefly explained. However, more details can be found from theco-pending UK applications identified above.

FIG. 5 provides a schematic diagram illustrating an LTE downlinksub-frame which includes a virtual carrier inserted in a host carrier inaccordance with an example of the present invention.

In keeping with a conventional LTE downlink sub-frame, the first nsymbols (n is three in FIG. 5) form the control region 300 which isreserved for the transmission of downlink control data such as datatransmitted on the PDCCH. However, as can be seen from FIG. 5, outsideof the control region 300 the LTE downlink sub-frame includes a group ofresource elements below the central band 310 which form a virtualcarrier 501. As will become clear, the virtual carrier 501 is adapted sothat data transmitted on the virtual carrier 501 can be treated aslogically distinct from the data transmitted in the remaining parts ofthe host carrier and can be decoded without first decoding all thecontrol data from the control region 300. Although FIG. 5 shows thevirtual carrier occupying frequency resources below the centre band, ingeneral the virtual carrier may be at any suitable location within thehost carrier 320. for example, above the centre band and/or in afrequency range overlapping with the centre band.

As can be seen from FIG. 5, data transmitted on the virtual carrier 501is transmitted across a limited bandwidth. This could be any suitablebandwidth providing it is smaller than that of the host carrier. Thisenables low capability terminals (for example MTC type terminals) to beprovided with simplified receiver units yet still be able to operatewithin a communication network which, as explained above, conventionallyrequires terminals to be equipped with receivers capable of receivingand processing a signal across the entire bandwidth of the carrier.

Also, as can be seen in FIG. 5, the final symbols of the virtual carriercan be reserved as a virtual carrier control region 502 which isallocated for the transmission of control data indicating which resourceelements of the virtual carrier 501 have been allocated. The virtualcarrier control region can be located at any suitable position withinthe virtual carrier for example in the first few symbols of the virtualcarrier. In the example of FIG. 5 this could mean positioning thevirtual carrier control region on the fourth, fifth and sixth symbols.However, fixing the position of the virtual carrier control region inthe final symbols of the sub-frame can provide an advantage because theposition of the virtual carrier control region need not vary even if thenumber of symbols of the host carrier control region varies. Thissimplifies the processing undertaken by mobile communication terminalsreceiving data on the virtual carrier because there is no need for themto determine the position of the virtual carrier control region everysub-frame as it is known that it will always be positioned in the finalsymbols of the sub-frame.

Optionally, the virtual carrier control symbols may reference virtualcarrier transmissions in a separate sub-frame.

In some examples the virtual carrier may be located within the centreband 310 of the downlink sub-frame. This would minimise the reduction inhost carrier PDSCH resources caused by the insertion of a virtualcarrier since the resources occupied by the PSS/SSS and PBCH would becontained within the virtual carrier region and not the host carrierPDSCGH region. Therefore, depending on for example the expected virtualcarrier throughput, the location of a virtual carrier can beappropriately chosen to either exist inside or outside the centre bandaccording to whether the host or virtual carrier is chosen to bear theoverhead of the PSS, SSS and PBCH.

FIG. 6 shows a flow diagram illustrating a camp-on process for a virtualchannel. In the example of FIG. 6, the first steps 400 and 401 are thesimilar to the conventional camp-on process shown in FIG. 4. At step606, the virtual carrier terminal locates a virtual carrier, if any isprovided within the host carrier. Once the virtual carrier terminal haslocated a virtual carrier, it can access information within the virtualcarrier. For example, if the virtual carrier mirrors the conventionalLTE resource allocation method, the virtual carrier terminal may thendecode control portions within the virtual carrier, which can forexample indicate which resource elements within the virtual carrier havebeen allocated for a specific virtual carrier terminal or for systeminformation. For example, FIG. 7 shows the blocks of resource elements350 to 352 within virtual carrier 330 that have been allocated for thesub-frame SF2. As discussed above, the virtual carrier terminal has tolocate the virtual carrier before it can receive and decode the virtualcarrier transmissions. Several options are available for the virtualcarrier presence and location determination, which can be implementedseparately or in combination. Some of these options are discussed below.

To facilitate the virtual carrier detection, the virtual carrierlocation information may be provided to the virtual carrier terminalsuch that it can locate the virtual carrier, if any exists, more easily.For example, such location information may comprise an indication thatone or more virtual carriers are provided within the host carrier orthat the host carrier does not currently provide any virtual carrier. Itmay also comprise an indication of the virtual carrier's bandwidth, forexample in MHz or blocks of resource elements. Alternatively, or incombination, the virtual carrier location information may comprise thevirtual carrier's centre frequency and bandwidth, thereby giving thevirtual carrier terminal the exact location and bandwidth of any activevirtual carrier. In the event that the virtual carrier is to be found ata different frequency position in each sub-frame, according for exampleto a pseudo-random hoping algorithm, the location information can forexample indicate a pseudo random parameter. Such parameters may includea starting frame and parameters used for the pseudo-random algorithm.Using these pseudo-random parameters, the virtual carrier terminal canthen know where the virtual carrier can be found for any sub-frame.

Depending on the amount of virtual carrier location informationprovided, the virtual carrier terminal can either adjust its receiver toreceive the virtual carrier transmissions, or it may require furtherlocation information before it can do so.

If for example, the virtual carrier terminal was provided with locationinformation indicating a virtual carrier presence and/or a virtualcarrier bandwidth but not indicating any details as to the exact virtualcarrier frequency range, or if the virtual carrier terminal was notprovided with any location information, the virtual carrier terminal canthen scan the host carrier for a virtual carrier (e.g. performing aso-called blind search process). Scanning the host carrier for a virtualcarrier can be based on different approaches, some of which will bepresented below.

As explained above, in LTE the number of symbols that make up thecontrol region of a downlink sub-frame varies dynamically depending onthe quantity of control data that needs to be transmitted. Typically,this variation is between one and three symbols. As will be understoodwith reference to FIG. 5, variation in the width of the host carriercontrol region will cause a corresponding variance in the number ofsymbols available for the virtual carrier. For example, as can be seenin FIG. 5, when the control region is three symbols in length and thereare 14 symbols in the sub-frame, the virtual carrier is eleven symbolslong. However, if in the next sub-frame the control region of the hostcarrier were reduced to one symbol, there would be thirteen symbolsavailable for the virtual carrier in that sub-frame.

When a virtual carrier is inserted into a LTE host carrier, mobilecommunication terminals receiving data on the virtual carrier need to beable to determine the number of symbols in the control region of eachhost carrier sub-frame to determine the number of symbols in the virtualcarrier in that sub-frame if they are to be able to use all availablesymbols that are not used by the host carrier control region.

Conventionally, the number of symbols forming the control region issignalled in the first symbol of every sub-frame in the PCFICH. However,the PCFICH is typically distributed across the entire bandwidth of thedownlink LTE sub-frame and is therefore transmitted on sub-carrierswhich virtual carrier terminals capable only of receiving the virtualcarrier cannot receive. Accordingly, in one embodiment, any symbolsacross which the control region could possibly extend are predefined asnull symbols on the virtual carrier, i.e. the length of the virtualsub-carrier is set at (m-n) symbols, where m is the total number ofsymbols in a sub-frame and n is the maximum number of symbols of thecontrol region. Thus, resource elements are never allocated for downlinkdata transmission on the virtual carrier during the first n symbols ofany given sub-frame.

Although this embodiment is simple to implement it will be spectrallyinefficient because during sub-frames when the control region of thehost carrier has fewer than the maximum number of symbols, there will beunused symbols in the virtual carrier.

In another embodiment, the number of symbols in the control region ofthe host carrier is explicitly signalled in the virtual carrier itselfIn one example an explicit indication of the host carrier control regionsize is given by certain information bits in the virtual carrier controlregion. In another example, the virtual carrier includes a predefinedsignal, the location of which indicates the number of symbols in thecontrol region of the host carriers. For example, a predefined signalcould be transmitted on one of three predetermined blocks of resourceelements. When a terminal receives the sub-frame it scans for thepredefined signal. If the predefined signal is found in the first blockof resource elements this indicates that the control region of the hostcarrier comprises one symbol; if the predefined signal is found in thesecond block of resource elements this indicates that the control regionof the host carrier comprises two symbols and if the predefined signalis found in the third block of resource elements this indicates that thecontrol region of the host carrier comprises three symbols.

In another example, the virtual carrier terminal is arranged to firstattempt to decode the virtual carrier assuming that the control regionsize of the host carrier is one symbol. If this is not successful, thevirtual carrier terminal attempts to decode the virtual carrier assumingthat the control region size of the host carrier is two and so on, untilthe virtual carrier terminal successfully decodes the virtual carrier.

As is known in the art, in OFDM based transmission systems such as LTE anumber of sub-carriers in each symbol are typically reserved for thetransmission of reference signals. The reference signals are transmittedon sub-carriers distributed throughout a sub-frame across the channelbandwidth and across the OFDM symbols. The reference signals arearranged in a repeating pattern and can thus be used by a receiver,employing extrapolation and interpolation techniques to estimate thechannel function applied to the data transmitted on each sub-carrier. InLTE the positions of the reference signal bearing sub-carriers withineach sub-frame are pre-defined and are therefore known at the receiverof each terminal.

In LTE downlink sub-frames, reference signals from each transmit antennaport are typically inserted on every sixth sub-carrier. Accordingly, ifa virtual carrier is inserted in an LTE downlink sub-frame, even if thevirtual carrier has a minimum bandwidth of one resource block (i.e.twelve sub-carriers) the virtual carrier will include at least somereference signal bearing sub-carriers.

There are sufficient reference signal bearing sub-carriers provided ineach sub-frame such that a receiver need not accurately receive everysingle reference signal to decode the data transmitted on the sub-frame.However, as will be understood the more reference signals that arereceived, the better a receiver will be able to estimate the channelresponse and hence fewer errors are typically introduced into the datadecoded from the sub-frame. Accordingly, in order to preservecompatibility with LTE communication terminals receiving data on thehost carrier, in some examples of the present invention, the sub-carrierpositions that would contain reference signals in a conventional LTEsub-frame are retained in the virtual carrier.

As will be understood, in some examples, terminals arranged to receiveonly the virtual carrier receive a reduced number of sub-carrierscompared to conventional LTE terminals which receive each sub-frameacross the entire bandwidth of the sub-frame. As a result, the reducedcapability terminals receive fewer reference signals over a narrowerrange of frequencies which may result in a less accurate channelestimation being generated.

In some examples a simplified virtual carrier terminal may have a lowermobility which requires fewer reference symbols to support channelestimation. However, in some examples of the present invention thedownlink virtual carrier includes additional reference signal bearingsub-carriers to enhance the accuracy of the channel estimation that thereduced capability terminals can generate.

In some examples the positions of the additional reference bearingsub-carriers are such that they are systematically interspersed withrespect to the positions of the conventional reference signal bearingsub-carriers thereby increasing the sampling frequency of the channelestimation when combined with the reference signals from the existingreference signal bearing sub-carriers. This allows an improved channelestimation of the channel to be generated by the reduced capabilityterminals across the bandwidth of the virtual carrier. In otherexamples, the positions of the additional reference bearing sub-carriersare such that they are systematically placed at the edge of thebandwidth of the virtual carrier thereby increasing the interpolationaccuracy of the virtual carrier channel estimates.

So far examples of the invention have been described generally in termsof a host carrier in which a single virtual carrier has been inserted asshown for example in FIG. 5. However, in some examples a host carriermay include more than one virtual carrier. For example FIG. 8 shows anexample in which two virtual carriers VC1 (330) and VC2 (331) areprovided within a host carrier 320 and change location within the hostcarrier band according to a pseudo-random algorithm. However, in otherexamples, one or both of the two virtual carriers may always be found inthe same frequency range within the host carrier frequency range and/ormay change position according to a different mechanism

In some examples the number of active virtual carriers can bedynamically adjusted such that it fits the current needs of conventionalLTE terminals and virtual carrier terminals. The network elements and/ornetwork operator can thus activate or deactivate the virtual carrierswhenever appropriate.

The virtual carrier shown for example in FIG. 5 is 144 sub-carriers inbandwidth. However, in other examples a virtual carrier may be of anysize between twelve sub-carriers to 1188 sub-carriers (for a carrierwith a 1200 sub-carrier transmission bandwidth). Because in LTE thecentre band has a bandwidth of 72 sub-carriers, a virtual carrierterminal in an LTE environment preferentially has a receiver bandwidthof at least 72 sub-carriers (1.08 MHz) such that it can decode thecentre band 310, therefore a 72 sub-carrier virtual carrier may providea convenient implementation option. With a virtual carrier comprising 72sub-carriers, the virtual carrier terminal does not have to adjust thereceiver's bandwidth for camping on the virtual carrier which maytherefore reduce complexity of performing the camp-on process, but thereis no requirement to have the same bandwidth for the virtual carrier asfor the centre band and, as explained above, a virtual carrier based onLTE can be of any size between 12 to 1188 sub-carriers.

In a situation where a virtual carrier is provided, there might beduplication of some data broadcasted to a mobile terminal in the hostcarrier and in the virtual carrier. For example, because the virtualcarrier is “hosted” in the host carrier, some of the system informationtransmitted in respect of the host carrier might be relevant forterminals in the virtual carrier. Because the two carriers are treatedas being logically independent, it is generally recognized that theduplication of such information is necessary and unavoidable to ensurethat each of the carriers is autonomous.

In a first example embodiment, the host carrier and virtual carrier mayeach comprise a grant or allocation information pointing to the samedata comprising broadcast and/or multicast information. Broadcast and/ormulticast information refers for example to information that is notunicast information. Unicast information is information that is sent toone specific terminal only.

For example, in FIG. 3, resource allocation 340 is for a terminalidentified as “UE 4” and is not for any other terminal. Such informationis sent as unicast information because it is sent to this terminal only.In that case, the control region comprises a PDCCH allocation message,also called “grant”, for the allocated resources 340, where this messagehas been scrambled with the RNTI for UE 4, where the RNTI is a uniqueidentifier for the terminal in at least the carrier, or the cell. Inanother example, also in FIG. 3, system information may be sent in acarrier, for example in the resources allocation 344. This is generallysent to all terminals in the cell using this carrier. In LTE, a PDCCHallocation message for system information is generally scrambled with asystem information RNTI (SI-RNTI) which is used to identify data sent toall terminals using this carrier. System information is an example ofbroadcasted information. It has to be noted that the base station orbase stations sending broadcast information may not know whether anyterminal will actually read the data in the allocated resources.

In the example of FIG. 9, where two sub-frames SF1 and SF2 have beenrepresented in the interest of conciseness, a virtual carrier 501 isprovided within a host carrier 320. In the second sub-frame SF2, systeminformation is broadcasted within the host carrier in the allocatedresources 344. It is generally expected that a resource allocationmessage, or grant, 301 may be found in the control region 301 of thehost carrier, the grant pointing to the allocated resources 344. In anexample of the present invention, an allocation message or grant 503 mayalso be found in the virtual carrier 501, e.g. in the control region 502of the virtual carrier. This grant 503 does not point to allocatedresources in the virtual carrier, as would be expected from such agrant, but, in this example, it points to allocated resources 344 in thehost carrier. In the example of FIG. 9, if a terminal using the virtualcarrier decodes the grant 503, the terminal may then decide either todecode —or continue decoding— data transmitted in the virtual channel orto re-configure its receiver to receive and decode the data (or somedata) transmitted in the allocated resources 344 comprising systeminformation. Thus, terminals using the host carrier and terminals usingthe virtual carrier can find and decode the system information requiredto communicate on both carriers using the same system information 344sent in the host carrier only.

In the event that the virtual carrier is provided with certainconstraints, for example a maximum bandwidth for the virtual carrier,some of these constraints may have to be applied to the allocatedresources that are being pointed to. For example, if a mobile networkprovides one or more virtual carriers for terminals having a receiverwith a capacity limited to 72 sub-carriers (i.e. the bandwidth of 6resource blocks), it may then be appropriate for the base station orbase stations providing the multicasted/broadcasted information to applythe same constraint to this multicasted/broadcasted information, i.e. inthat example the bandwidth of the multicasted/broadcasted informationwould be equal to or less than 72 sub-carriers.

In the example of FIG. 9, the multicasted/broadcasted information isprovided within the host carrier, however this multicasted/broadcastedinformation may also be provided within the virtual carrier, asillustrated in FIG. 10. In the example of FIG. 10, themulticasted/broadcasted information is system information sent in theallocated resources 344 where these allocated resources are providedwithin the virtual carrier 501. In that case, the virtual carrier 501comprises an allocation message or grant 503 pointing to the systeminformation 344 in the virtual carrier 501 in the next sub-frame. Where,in legacy systems, the host carrier 320 would only comprise allocationmessages or grant pointing to resources allocated in this host carrier,in the present example, the host carrier 320 also comprises anallocation message or grant 503 pointing to allocated resources 344containing system information and provided in the virtual carrier 501.This has the advantage that a terminal with limited bandwidth capabilityusing the virtual carrier will not need to retune its receiver to adifferent centre frequency in order to receive the system informationmessage. A terminal communicating via the host carrier 320 may forexample decode the grant 301 and, if the terminal decides to decode thesystem information in the allocated resources 344, the terminal simplydoes so according to the allocation message 301. Thus, terminals usingthe host carrier and terminals using the virtual carrier can find anddecode the system information sent in the virtual carrier only.

In the examples of FIGS. 11A, 11B and 11C, there has been shown twoexamples for providing the system information within the virtual carrier501. In the example of FIG. 11A, the system information uses all orsubstantially all the resources available in a sub-frame fortransmitting data in the virtual carrier. In this example, resources 502are reserved in a sub-frame to provide a control portion in the virtualcarrier. However in other examples, for example in FIG. 11B, there maynot be any resources reserved for the transmission of controlinformation. In that case, all or substantially all resources 344 in thevirtual carrier 501 for a sub-frame may be used for sending the systeminformation, where no resources have been reserved for any other use.

In the example of FIG. 11C, the system information 344 is sent in onlysome, but not all, of the resources available for transmitting data viathe virtual carrier 501 for this sub-frame. In that example, resources502 have also been reserved for sending control information however inother examples there may not be any resources reserved for controlinformation. Also, in the example of FIG. 10, the virtual carrierallocation message 503 pointing to the system information was providedin the sub-frame preceding the sub-frame providing this systeminformation. In the example of FIG. 11C, the grant 503 may be providedin the same sub-frame as the system information that it points to, asillustrated by the arrow pointing from the resource allocation 503 tothe system information 344. Such an example is similar to the exampleillustrated in FIG. 12, where the grant 503 is provided in the samesub-frame as the system information. In the example of FIG. 12, it hasnot been detailed how the system information is provided within the hostcarrier. It may for example be similar to the illustrations of FIGS.11A-11C, or provided differently.

The system information 344 may also be provided in the virtual carrier501 in a manner similar to that illustrated in FIG. 10, that is with theresource allocation 503 being provided in the, or a, previous sub-frame.For example, the grant 503 of 11C might actually be pointing tomulticasted/broadcasted information or to unicast information in the, ora, next sub-frame.

There has therefore been provided a system and method where terminalscan use a host carrier or a virtual carrier provided within the hostcarrier to receive data, where the two carriers are provided in anautonomous manner, where information which is of interest to terminalsin the virtual carrier and in the host carrier can be provided onceonly, and where a grant or resource allocation is provided in one of thecarrier and points to the information provided in the other carrier. Asa result, the number of resources allocated for transmitting themulticast/broadcast information can be reduced, thereby improving thethroughput and efficiency of the carriers.

Multiple Carriers Example

In another example, at least two carriers are provided where the twocarriers do not overlap in range and are provided in two separatefrequency ranges. An example of two such carriers is illustrated in FIG.13. Two carriers 1210 and 1230 are provided in two different frequencybands where mobile terminals may use one or both of the carriers inorder to receive data transmitted by one or more base stations via thetwo carriers 1210, 1230. It may be for example that a mobile terminalcan use each one of the carriers in a conventional mobile networkarrangement, that is, the carrier can be the only downlink carrier viawhich the mobile terminal receives data from the one or more basestations. For example in the initial releases of the LTE standard, aterminal communicating with a base station usually receives downlinkdata via one, and only one, downlink carrier. This carrier could forexample be “carrier 1” 1210 or “carrier 2” 1230. In a non-conventionalsituation where a terminal is connected to two (or more) carriers, forexample carriers 1210 and 1230, the terminal receives data from bothcarriers at the same time. Such a terminal can therefore experience anenhanced throughput as it may for example receive at least twice as muchdata with two carriers rather than one.

Also, as any carrier that may be used as a terminal's only downlinkcarrier has to provide an autonomous carrier for that terminal, each ofthe carriers 1210 and 1230 has to provide any terminal using thiscarrier only with any information they need for using this carrier. As aresult, conventionally, allocated resources in one carrier correspondsto an allocation message or grant in the same carrier, in a one-to-onerelationship. For example, in FIG. 13, resources 1222 and 1223 allocatedfor system information and sent in the first carrier 1210 have onecorresponding allocation message 1212 and 1213, respectively, so thatterminals using the first carrier can find the system information forthis carrier. Likewise, the second carrier 1230 comprises resources 1242allocated for system information and a corresponding allocation message1232 so that terminals using the second carrier can find and decode thesystem information. The choice of system information is purelyillustrative, as the allocated resources may be for any type of data forone or more terminals. For example, the resources may be allocated foranother type of broadcasted or multicasted data such as TV data 1243which is associated with an allocation message 1233. In another examplethe transmitted data may be data transmitted for one terminal only(unicast data) as illustrated by the allocated resources 1244 for oneterminal identified as “UE 1”. Again, the allocated resources 1244 areassociated with an allocation message or grant 1234 pointing to theallocated resources.

In one example shown in FIG. 14, resources 1245 allocated for systeminformation is provided in a sub-frame of the second carrier 1230. Theallocated resources 1245 in the second carrier is associated with agrant or allocation message 1235 in the same carrier, that is, in thesecond carrier. Advantageously, if resources allocated in the secondcarrier comprise information for terminals in the first carrier, thefirst carrier may also comprise a grant or allocation message associatedwith the allocated resources in the second carrier. Thus, in the exampleof FIG. 14, if the resources 1235 allocated to system informationcomprise information in respect of the first carrier 1210, a terminalusing the first and second carriers may be directed to systeminformation in the second carrier by the grant 1215 provided in thefirst carrier.

In another example (not shown), a terminal arranged to use the first andsecond carriers may be in a waiting or idle state and listening to apaging channel on the first or second carrier. For the ease ofillustration, it will be assumed that the terminal is listening to apaging channel on the first carrier, however the same reasoning appliesequally if the terminal is listening to the second carrier. Even thoughthe terminal is listening to the first carrier, the one or more basestations providing the first and second carriers may not know which ofthe first and second carriers' paging channel the terminal is listeningto. Using conventional LTE or conventional mobile systems, the one ormore base stations would page the terminal on both the first and secondcarriers, thereby using twice the paging resources that would be used ifpaging the terminal on the carrier's paging channel it is listening to.In an arrangement similar to the arrangement shown in FIG. 14, the oneor more base stations may use only paging channel for paging theterminal, for example a paging channel in the second carrier 1230, andinclude two grants associated with this paging channel: one grant beingin the first carrier 1210 and a second grant being in the second carrier1230. As a result, the terminal is guaranteed to find the pagingchannel, whichever carrier it is provided in, and whichever carrierand/or channel the terminal may be listening to, whilst the resourcesused for paging the terminal have been reduced by half.

Each carrier may provide independent broadcasted/multicasted information(e.g. system information for one carrier only), nobroadcasted/multicasted data, and/or common broadcasted/multicastedinformation (e.g. system information for two or more carriers). Forexample, in the illustration of FIG. 15, the first carrier 1210 providesa first sub-frame system information data 1226 that comprises data ofinterest for terminals using the first and the second carriers. Thefirst and second carriers 1210 and 1230 both provide a correspondingallocation message 1216 and 1236, respectively, in their control portion1211 and 1231, respectively. In this example, in the next sub-frame eachof the first and second carriers 1210 and 1230 provide systeminformation data 1227 and 1245, respectively, for terminals using thiscarrier only. Because the system information in a carrier is forterminals using this carrier only, it would be inefficient to include anallocation message in the other carrier and pointing to the systeminformation data. Thus in this example, the first and second carriers1210 and 1230 provide allocations messages 1217 and 1235, respectively,pointing to their respective multicasted and/or broadcasted systeminformation data 1227 and 1245.

In other examples (not illustrated), the control portion 1211 of thefirst carrier 1210 for the second sub-frame may also include a grant orallocation message associated with the system information 1245 in thesecond carrier 1230.

As previously explained, any broadcasted or multicasted information maybe associated with multiple allocation messages provided in at least twocarriers. The example of FIG. 16 shows a possible combination of TV databroadcasted or multicasted in the first carrier 1210 and systeminformation broadcasted or multicasted in the second carrier 1230. Inthat example, TV data 1226, 1227 is provided in the first carrier 1310in the first and second sub-frames and system information 1245 isprovided in the second carrier 1330 in the second sub-frame. Each of theresources 1226 and 1227 allocated for TV data is associated with twoallocation messages 1216, 1236 and 1217, 1237 respectively. Thus, anyterminal using the first carrier 1210 or the second carrier 1230 isprovided with an allocation message pointing to the TV data in the firstcarrier 1210 and can access the TV data if using the two carriers. Forexample, if an operator wishes to have a carrier dedicated for certainbroadcast services, such as Multimedia Broadcast Multicast Service(MBMS), TV services, or any other type or broadcasted or multicastedservices, the operator can dedicate the first carrier to such services,and use the second carrier as a conventional carrier. Conventional andlow-end terminals may then use the second carrier in a conventionalmanner while more advanced terminals may use the first carrier for thesecertain services and the second carrier for all services except thesecertain services, possibly using both carriers at the same time.

In the example of FIG. 16, there is also provided system information1245 broadcasted in the second sub-frame of the second carrier 1230 thathas two grants 1215 and 1235 associated with it, the first one being inthe first carrier 1210 and the second one being in the second carrier1230.

Also, generally the examples have been illustrated where one block ofallocated resources in one sub-frame is associated with (at least) onegrant in the same sub-frame. However, the invention is not limited tothat arrangement and, for example, the grant or allocation message maybe in another sub-frame and/or there may be less or more allocationmessages per sub-frame than blocks of allocated resources. For example,FIG. 17 illustrates an example where one grant 1238 in the secondcarrier 1230 is associated with at least three blocks of resources forTV in the second carrier 1230 and one grant 1248 in the first carrier1210 is associated with at least three blocks of resources for TV 1248a, 1248 b, 1248 c in the first carrier. For example, the resources maybe changing from sub-frame to sub-frame in pseudo-random fashion and onegrant may be sufficient for indicating the position of the resourcesallocated for a service or a user for more than one sub-frame.

As illustrated in FIG. 18, broadcasted or multicasted informationassociated with multiple allocation messages provided in at least twocarriers may be partitioned in parts comprising information forterminals in one carrier and/or parts comprising information forterminals in one carrier in a set of carriers, wherein a set of carriersis a group of any two or more carriers. In the example of FIG. 18, thecommon information (broadcasted or multicasted information) comprises apart for information common to two carriers C1 and C2, a part forinformation in respect of carrier C1 and a part for information inrespect of C2. In this example, each part represents 70%, 20% and 10% ofthe resources allocated to the common information, respectively. Howevereach of these parts may represent any suitable percentage of theresources allocated to the common information in the 0%-100% range.Also, if the broadcasted or multicasted information comprisesinformation for more than two carriers, the common information may bepartitioned in any appropriate manner so that relevant information inrespect of these two or more carriers can be included in the commoninformation.

Also, the partitioning of the common information may be fixed or mayvary. For example it may vary on a per frame basis, or based on a numberin each carrier of terminals which will possibly access the commoninformation, or based on any other suitable factor or parameter.

Also, the examples shown in the accompanying Figures are forillustration only and are not limiting. For example, the allocatedresources may not extend across the entirety of resources available fordata transmission in a sub-frame, as illustrated with 1222, 1223, 1242,1243 and 1244 of FIG. 13, but may only extend across a portion of theseavailable resources as illustrated with allocated resources 1224 of FIG.13. Also, the allocation message in a carrier has generally been shownin the same sub-frame as the allocated resources of the same carrier,for example grant 1214 and resources 1224, as this is the conventionalrelative arrangement of allocation messages and allocated resources inLTE, however the grant may be in a different sub-frame to the allocatedresources.

Likewise, the examples generally show two carriers in order toillustrate the invention, however the invention is not limited to twocarriers and any number of carriers equal or higher than two can besuitable for using the invention.

Generally, the invention has been described in an LTE environment as theinvention can be advantageously implemented in this environment, howeverthe invention is not limited to an LTE environment and may beimplemented in any other suitable environment.

CONCLUSION

Various modifications can be made to examples of the present invention.Embodiments of the present invention have been defined largely in termsof reduced capability terminals transmitting data via a virtual carrierinserted in a conventional LTE based host carrier. However, it will beunderstood that any suitable device can transmit and receive data usingthe described virtual carriers for example devices which have the samecapability as a conventional LTE type terminal or devices which haveenhanced capabilities.

Likewise, system information is only an example ofbroadcasted/multicasted information used in illustrative embodiments andthe invention is not limited to system information. In fact, anysuitable type of information may be used with the invention. Such typesof information may for example also include paging, TV services, MBMS,group information, etc.

Furthermore, in all embodiments, each carrier may provide independentbroadcasted/multicasted information (e.g. system information for onecarrier only), no broadcasted/multicasted data, and/or commonbroadcasted/multicasted information (e.g. system information for two ormore carriers).

Furthermore, it will be understood that the general principle ofinserting a virtual carrier on a subset of uplink or downlink resourcescan be applied to any suitable mobile telecommunication technology andneed not be restricted to systems employing an LTE based radiointerface.

1. A network apparatus for communicating data to and/or from mobile units, the apparatus being arranged to: provide a wireless access interface within one or more frequency bands to communicate data to or from the mobile units; provide a plurality of logically separate carriers for transmitting data to mobile units, wherein a carrier comprises physical resources within the one or more frequency bands of the wireless access interface, wherein the apparatus is further arranged to provide a first carrier of the plurality of carriers to communicate with a first group of one or more mobile units and a second carrier of the plurality of carriers to communicate with a second group of one or more mobile units; provide common information on the first carrier, the common information being for at least one mobile unit in the first group and for at least one mobile unit in the second group; provide allocation information in the first carrier, the allocation information comprising an indication of the location of the common information within the first carrier; and provide allocation information in the second carrier, the allocation information comprising an indication of the location of the common information within the first carrier.
 2. A network apparatus according to claim 1, wherein the common information provided by the apparatus comprises a first portion common to mobile units of the first group and of the second group, and further comprises a second portion comprising information for one or more mobile units of the first group.
 3. A network apparatus according to claim 2, wherein the common information provided by the apparatus further comprises a third portion comprising information for one or more mobile units of the second group.
 4. A network apparatus according to claim 1, wherein the common information provided by the apparatus comprises system information in respect of the first carrier and/or second carrier.
 5. A network apparatus according to claim 1, wherein the common information provided by the apparatus comprises paging information for one or more mobile units of the first group and/or second group.
 6. A network apparatus according to claim 1, wherein the common information provided by the apparatus comprises data for a broadcast and/or multicast service.
 7. A network apparatus according to claim 6, wherein the common information provided by the apparatus comprises Multimedia Broadcast Multicast Service data.
 8. A network apparatus according to claim 1, the apparatus being arranged to transmit data on the downlink in time-adjacent sub-frames; and wherein one of the allocation information in the first carrier and the allocation information in the second carrier is in a sub-frame preceding a sub-frame of the common information.
 9. A network apparatus according to claim 1, wherein the frequency range of the second carrier is smaller and within the frequency range of the first carrier.
 10. A network apparatus according to claim 9, the apparatus providing the second carrier such that the bandwidth of the second carrier does not exceed a maximum bandwidth and wherein the apparatus operable to provide the common information in the first carrier comprises the apparatus operable to provide the common information within a frequency range having a bandwidth equal to or smaller than the maximum bandwidth of the second carrier.
 11. A network apparatus according to claim 1, wherein the frequency range of the first carrier is smaller and within the frequency range of the second carrier.
 12. A network apparatus according to claim 11, wherein the apparatus is arranged to transmit data on the downlink in time-adjacent sub-frames; and wherein the allocation information in the second carrier is provided in the same sub-frame as a sub-frame of the common information.
 13. A network apparatus according to claim 1, wherein the frequency range of the first carrier and the frequency range of the second carrier do not overlap.
 14. A network apparatus according to claim 1, wherein the apparatus comprises at least one of a base station and a radio network controller. 